1. Field of the Invention
The present invention relates to an ultrasonic flaw detector for use in combination with a wiredrawing apparatus for drawing a linear work, such as a metal rod or wire, through a die to reduce its cross section.
2. Description of the Related Art
In a cold wiredrawing process, in general, a linear work, such as a metal rod or wire, is lubricated by a lubricant before being drawn through a drawing die. Flaws in the linear work are detected by an ultrasonic flaw detector or an eddy-current flaw detector during the cold wiredrawing process. In such a conventional wiredrawing process, the ultrasonic flaw detector is disposed, generally, between the die box and wire feeder of the wiredrawing apparatus, and an inlet guide and an outlet guide are provided, respectively, at the inlet end and outlet end of the ultrasonic flaw detector to prevent eccentricity of the linear work relative to the ultrasonic flaw detector. The ultrasonic flaw detector is provided with a normal probe and a sectional angle beam probe, which are provided within an ultrasonic testing tank, to detect mainly inclusions in the interior and under the skin of the linear work.
Such a conventional ultrasonic flaw detector for a wiredrawing apparatus requires a space for installation between the die box of the wiredrawing unit and the wire feeder and hence it is difficult to form the wiredrawing apparatus in a compact construction, flaws in the drawn wire cannot be detected because the ultrasonic flaw detector is disposed before the die box (In the following description, words for forming positional phrases, such as "before", "after", "front" and "rear", are used for denoting the sequential position of one thing relative to another with respect to the running direction of the linear work and the drawn wire.) and hence the the drawn wire drawn by a final wiredrawing process must be subjected to a separate ultrasonic testing process.
Ultrasonic flaw detection tests were performed by using the conventional ultrasonic flaw detector, in which the ultrasonic flaw detector was disposed next to the die box of a wiredrawing machine. The results of the tests showed that the lubricant applied to the linear work before wiredrawing comes off the drawn wire in flakes, the flakes of the lubricant drifted in the ultrasonic testing medium (water or oil) contained in the ultrasonic testing tank to disturb flaw detection signals, and hence accurate ultrasonic testing could not be achieved.
Although the conventional ultrasonic flaw detector having, contained in the ultrasonic testing tank, only the normal probe and the sectional angle beam probe is able to detect internal defects, such as inclusions in the interior and under the skin of the drawn wire, the conventional ultrasonic flaw detector is unable to detect chevron cracks having a substantially conical shape tapering in the drawing direction, which are internal defects occurring in drawn steel wires.